A conventional gas turbine engine combustor includes radially spaced outer and inner combustor liners joined at an upstream end thereof by a dome assembly. The dome assembly includes a plurality of circumferentially spaced carburetors therein, with each carburetor including a fuel injector for providing fuel and an air swirler for providing swirled air for mixing with the fuel for creating a fuel/air mixture discharged into the combustor between the two liners. The mixture is conventionally burned for generating combustion gases which flow downstream through the combustor to a conventional turbine nozzle suitably joined to the downstream end of the combustor. Immediately downstream of the turbine nozzle is a conventional high-pressure turbine which extracts energy from the combustion gases for powering a compressor disposed upstream of the combustor which provides compressed air to the air swirlers.
A significant performance consideration for the combustor is the conventionally known pattern factor which is a nondimensional factor indicative of temperature distribution to the turbine nozzle. The pattern factor may be defined as the maximum temperature of the combustion gases at the combustor outlet minus the average temperature thereof divided by the average outlet temperature minus the temperature of the compressed air at the inlet to the combustor. The pattern factor indicates the relative uniformity of combustion gas temperature experienced by the turbine nozzle from the combustor outlet, with an ideal pattern factor of zero indicating uniform temperature.
In one conventional gas turbine engine combustor, it was desirable to increase the combustor outlet temperature for increasing power output from the gas turbine engine. Although the pattern factor for the increased power combustor was the same as the original combustor, the increased maximum combustor outlet temperature would have led to a reduction in turbine life. Accordingly, modifying the original combustor for reducing pattern factor was desired for improving turbine life.
Accordingly, a conventional air swirler known to have a relatively low pattern factor was scaled down from an engine having a dome height of about two and one-half inches (about six centimeters) for the above combustor having a dome height of about one and one-half inches (about four centimeters). The air swirler from the original combustor and the one to be used as a replacement air swirler were both conventional counterrotational air swirlers, the former having a primary venturi throat diameter of about two-thirds that of the latter. However, it was determined analytically that simple scaling down of the low pattern factor air swirler could not result in similar low pattern factor in the original combustor since the original manufacturing tolerances were already at a minimum of about 1 mil. In view of the relatively small size of the original combustor, manufacturing tolerances prevented the attainment of the required relatively low pattern factor for improving life of the combustor and the turbine. The original combustor had a particular, or first reference pattern factor, and the replacement air swirler having a smaller, or second reference pattern factor in its larger size application would have been unable to attain significantly reduced pattern factor in the smaller combustor size.
Another significant consideration in the design of the gas turbine engine combustor is serviceability of the life-limiting parts therein. For example, the dome assembly includes a conventional baffle extending from the air swirler and spaced from the combustor dome for providing a channel therebetween for channeling compressor air for cooling at least the baffle itself. The baffle provides a heat shield between the combustion occurring immediately downstream of the air swirler for protecting the dome. Accordingly, it is one life-limiting part which is replaced at periodic intervals.
The baffle is typically welded and/or brazed to the dome and typically requires replacement of the entire dome assembly therewith or substantial disassembly work at the periodic service intervals. Such baffle replacement service is relatively expensive and requires a significant amount of time.